I couldnt agree more. You make an excellent point. It is not hard for them to ride in a single file. If they would like to socialize maybe they should do it after their bike ride. Arastradero is also a major problem. People do not realize how dangerous this road is for bikers and cars. I have friends who are professional cyclists that avoid Arastradero for this exact reason, even though it is very beautiful. Unfortunately Nadir, it seems like this situation calls for the police to be stationed at different areas of Portola Rd and Alpine during the weekends to enforce these laws, but I dont think the San Mateo Sheriff has the resources or the man power to divert to this every weekend. And to all of the safe cyclists out there: THANK YOU FOR BEING CONSIDERATE OF EVERYONE!